Hydrocracking of hydrocarbons with the constant addition of sulfur to the reaction zone



United States Patent 3,395,095 HYDROCRACKING 0F HYDROCARBONS WITH THECONSTANT ADDITION OF SULFUR TO THE REACTION ZONE Edward T. Child,Fishkill, Donald A. Messing, Poughkeepsie, and Reese A. Peek, Fishkill,N.Y., assignors to Texaco Inc, New York, N.Y., a corporation of DelawareNo Drawing. Filed July 1, 1965, Ser. No. 468,932 3 Claims. (Cl. 208-111)This invention relates to the hydroconversion of hydrocarbons. Moreparticularly, it is concerned with the conversion of heavy hydrocarbonliquids into lighter hydrocarbon liquids. In its more specific aspectsit relates to the hydroconversion of hydrocracking of hydrocarbonliquids boiling above about 400 F. into hydrocarbon liquids boilingbelow about 400 F.

Hydrocracking, that is the cracking in the presence of hydrogen ofpetroleum hydrocarbons for the production of motor fuels and jet fuels,is well known. It is also known to carry out the reaction in thepresence of a catalyst which is conventionally composed of twocomponents, a cracking component which forms the major portion of thecatalyst composite and a hydrogenating component which generally issupported on the cracking component. Suitable hydrogenating componentscomprise the metals of Group VI and Group VIII such as, for example,nickel, iron, tungsten, cobalt, palladium, platinum, molybdenum, theiroxides or sulfides, and mixtures thereof. Particularly suitablehydrogenating components comprise nickel and palladium.

The hydrogenating component generally is present in the catalystcomposite in an amount between about 0.1 and 40% by weight and issupported on a carrier having cracking activity. Supports such asnatural cracking catalysts, synthetic silica alumina, synthetic silicamagnesia, montmorillonite clay, alumina gel, silica gel and natural andsynthetic zeolites are satisfactory. Advantageously the support iseither naturally acidic or has had cracking activity imparted thereto bytreament with an acid such as hydrofluoric acid. A silica-aluminasupport containing between 8090% silica and -20% alumina or a syntheticzeolite having a low alkali metal content has been found particularlysuitable. The catalysts, depending on their composition and ruggedness,may be used in fixed, moving or fluidized beds.

In known hydrocracking processes it is customary to pass a feed havingan initial boiling point higher than the end point of the desiredproducts into contact with a fixed bed composed of particles ofhydrocracking catalyst. The desired fractions are recovered from thereaction products and unconverted or insufficiently converted materialmay be withdrawn from the system or returned to the reaction zone. Forthe most part the desired reaction products of a hydrocracking processare motor fuels and jet fuels.

However, the hydrocracking processes of the prior art are relativelyinflexible. By this is meant that when a plant is designed for theproduction of jet fuels it is equipped to produce only jet fuelseconomically and if it is designed for the production of gasoline, it isequipped to give good yields only of gasoline economically. As a resultwhen a plant is designed to produce jet fuel it is inadvisable for therefiner to change to gasoline production despite what the marketingsituation might be at that particular time. This means that a plantusing a catalyst which is designed to produce jet fuel must continue todo so although there is an over supply of that commodity. The same holdtrue for gasoline. Plants designed to produce motor fuel are 3,395,095Patented July 30, 1968 not justified in changing to the production ofjet fuel as the jet fuel so produced is of an inferior grade.

The problem is not merely a question of fractionating from thehydrocracked product a fraction boiling in the gasoline range or afraction boiling in the jet fuel range as the case may be. The realproblem lies in the production of these fuels having suitableproperties. For example, when a hydrocracking plant is designed toproduce jet fuels, the jet fuel product is of high quality but the motorfuel fraction is of low grade. Similarly when a hydrocracking plant isdesigned to produce high octane motor fuel then the jet fuel fractionproduced simultaneously is unsatisfactory in that it does not meet jetfuel specifications.

It is an object of the present invention to provide a flexiblehydrocracking process. Another object is to provide a process for theproduction of jet fuels and/ or motor fuels of high quality without ineffect changing the catalyst. These and other objects will be obvious tothose skilled in the art from the following disclosure.

According to the present invention a hydrocarbon liquid fraction boilingabove about 400 F. is converted into valuable products by contactingsame under hydrocrack ing conditions with a hydrocracking catalystcontaining a hydrogenating component comprising a Group VIII metal ormetal oxide, recovering from the reaction product a fraction boiling inthe motor fuel range, recycling to the hydrocracking zone a productfraction boiling above the motor fuel range, introducing sulfurcompounds into the hydrocracking reaction zone, continuing said recycleuntil about 60-80% of the metal of the hydrogenating component has beenconverted to the sulfide and then recovering from the reaction product ahydrocarbon fraction boiling through the jet fuel range.

If it is intended to produce gasoline over an extended period of timethen both the charge stock and the hydrogen should be substantiallysulfur free to preserve the catalyst in its unsulfided form. This may bedone by a preliminary desulfurization treatment of the charge stock in awell-known manner with a catalyst comprising nickel and/ or cobalt andmolybdenum in the presence of hydrogen. If hydrogen from thedesulfurization step is used in the hydrocracking stage, it is advisableto treat the hydrogen for the removal of H 8 such as by scurbbing withethanolamine or by contacting the hydrogen with a bed of zinc oxide.

When it is desired to produce jet fuel the preliminary desulfurizationstep can be eliminated and the sulfur containing charge stock can beintroduced directly into the hydrocracking zone. The sulfur compoundspresent in the charge stock will gradually convert the catalyst to thesulfide form and the initial boiling point of the recycled product canthen be increased from about 400 F. to about 550 F. However, it has beenfound advantageous to employ an initial or preliminary step to reducenitrogen and sulfur levels regardless of the type of product fueldesired as certain other benefits are derived therefrom such as thesaturation of olefins and polycyclic aromatics thus facilitating thesubsequent hydrocracking reaction.

When the preliminary desulfu'rization step is employed and it is desiredto start the production of jet fuel then the hydrocracking catalyst canbe converted to the sulfide form either by using hydrogen sulfidecontaining off-gas from the desulfurizati'on stage or in the alternativeif hydrogen being used in the hydrocracking zone is substantially sulfurfree, by adding sulfur containing compounds either to the hydrogen or tothe hydrocarbon charge stock. Suitable sulfur containing compounds are H8, CS and low molecular weight mercaptans or sulfides such as butylmercaptan and tertiary butyl sulfide. A particularly advantageous methodof operation is to commence production of motor fuel using an unsulfidedcatalyst, charging hydrocarbon and scrubbed hydrogen from a desulfurization unit to the hydrocracking zone and permitting the residualsulfur present in the charge stock to gradually convert the catalyst tothe sulfide form. In this way, motor fuel is produced while the catalystis in the unsulfided state and product boiling above the motor fuelrange is recycled to the hydrocracking zone until the catalyst becomessulfided. Thereafter a jet fuel fraction boiling above the motor fuelfraction is also recovered as product. The recovered jet fuel fractionis superior to that obtained when the catalyst is in the unsulfidedstate and the gasoline produced when the catalyst is in the unsulfidedform is superior to that produced with a sulfided catalyst.

The process of the present invention has its greatest application in thetreatment of hydrocarbon fractions boiling above the motor fuel rangefor example boiling in the range of about 400 F. to about 900 F.although fractions having an initial boiling point as low as 200 F. maybe satisfactorily treated. Suitable charge stocks include straight rungas oils, fluid catalytic cracking cycle gas oils, deasphalted oil,coker distillate gas oil and the like. Cycle oils and cycle oil extractsfrom catalytic cracking are particularly desirable. Suitable chargestocks are obtained from crude petroleum oils, shale oil, tar sand oil,oils derived from coal and the like.

As pointed out above if the charge stock contains sulfur compounds andit is desired to maintain the production of motor fuel over an extendedperiod of time then the charge stock should be subjected to apreliminary desulfurization. This can be accomplished by a variety ofmethods known in the art, a preferred method comprising charging thehydrocarbon feed to a catalytic desulfurization zone containing a cobaltmolybdate on alumina catalyst at a temperature of about 650 F., apressure of about 500 p.s.i.g., a hydrogen recycle rate of about 5000-6000 s.c.f.b. and a liquid hourly space velocity between about 1 and 2.Such treatment will generally effect about a 70 to 80% reduction in thesulfur content of the charge. The remaining amount of sulfur issufiicient over a prolonged .period of time to gradually convert thehydrocracking catalyst to the sulfide form after which the initialboiling point of the recycle product stream can be increased from about400 F. to about 550 F. However, this period of time can be shortened orextended by varying the severity of the desulfurization reaction. Theaddition of sulfur containing compounds to the hydrocracker feed alsoresults in a shorter period.

Hydrogen used in the process of the present invention may be obtainedfrom any suitable source. The hydrogen need not be pure but may containas much as 40% impurities. In this respect the term hydrogen as used inthe specification and claims includes dilute hydrogen. The hydrogen neednot be free from sulfur compounds but the presence of sulfur in thehydrogen should be controlled in accordance with the end productdesired. If gasoline or motor fuel is the principal end product then thehydrogen should be relatively free from sulfur, but if it is desired toconvert from the production of gasoline to jet fuel then advantageouslythe hydrogen will contain sulfur compounds the amount bearing directlyon when the conversion is to take place. Suitable sources of hydrogenare catalytic reformer byproduct gas, electrolytic hydrogen and hydrogenobtained from the partial oxidation of carbonaceous material followed byshift conversion and CO removal.

The hydrocracking reaction is carried out at a temperature between about500 and 850 F., preferably 550- 800 F. Preferably the pressure ismaintained within the range of 1000 to 3500 p.s.i.g. although pressuresfrom 500 to 10,000 p.s.i.g. and higher may be used. Hydrogen rates from1000 to 20,000 s.c.f.b. of charge stock are satisfactory althoughhydrogen rates of 3000 to 8000 s.c.f.b. are preferred. Space velocitiesthat is the volumes of liquid charge per volume of catalyst per hour mayrange between 0.1 and 10 but preferably are within the range of 0.5-2.

The catalysts used in the process of the present invention comprise twocomponents, a hydrogenation component supported on a cracking component.As hydrogenating components the catalyst may contain from 0.5 to 40%preferably from about 5 to 20% by weight of a Group VI or Group VIIImetal such as chromium, tungsten, cobalt, nickel or mixtures thereof.The hydrogenating component is supported on a cracking base such as amixture of two or more difiicultly reducible oxides such assilica-alumina, silica-magnesia, silica-titania, silica-zirconia andnaturally occurring clays. The cracking properties of the base can beimproved 'by treatment with an acidic material such as HF. Aparticularly suitable base of this type is a co-precipitatedsilica-alumina containing for example about silica and 10-20% alumina.

Another type of support is a large pore zeolite, that is, a crystallinezeolite having uniform pore openings of about 6 to 15 Angstrom units.Zeolites of the X or Y type fall within this category. Advantageouslythese supports are prepared by subjecting a naturally occurring orsynthetic zeolite to an ion exchange treatment to replace the alkallimetals of the zeolite with hydrogen or divalent metal ions. Preferablythe alkali metal content of the zeolite is reduced to less than 10% byweight. In the case of the divalent metal the ion exchange can be madedirectly using a solution containing ions of the desired metal or can gothrough an intermediate stage in which the zeolite is in the hydrogenion form. The hydrogen ion form of the zeolite may be produced bytreating the zeolite with an acidic solution having a pH no less thanabout 3 although preferably the acid form of the zeolite is produced bytreating the zeolite with a. solution of ammonia, drying and thenheating to convert the ammonium ion form to the hydrogen ion form.

The hydrogenating component may be incorporated into the molecular sieveor zeolite support by means of impregnation or ion exchange or acombination of the two or into the conventional cracking catalystsupport by impregnation using a solution of a compound of thehydrogenating metal or metals. The catalyst is then drained, dried andcalcined to form the metal oxide. This form of the hydrogenatingcomponent may be charged as is to the hydrocracking zone or may beconverted to the metal form by contact with hot hydrogen, in which casethe reduction is preferably accomplished in the hydrocracking zone usingthe same reaction temperatures and pressures as are used during thehydrocracking reaction. Particularly suitable catalysts are a mixture ofnickel and tungsten on silica-alumina or on a molecular sieve.

In the course of carrying out the hydrocracking process, the catalystgradually loses its activity due to the formation of carbon thereon. Bythe time this happens, in a preferred embodiment of the invention, thecatalyst has already become sulfided and the unit is on jet fuelproduction. To regenerate the catalyst by removal of the carbon anoxidizing gas containing a carefully regulated amount of oxygen forcontrol of the catalyst temperature during the regenerative burning isintroduced into the hydrocracking zone. After regeneration the catalystwill be for the most part in the oxide form. When the on-stream periodis then begun, since the catalyst is in the oxide form, the productfraction boiling above the motor fuel range is recycled to thehydrocracking zone and the recycle of this fraction is continued untilthe catalyst is sulfided to such an extent that the operation is againconverted to jet fuel production.

The following example is submitted for illustrative purposes only.

A charge stock fluid catalytic cracking cycle gas oil having thefollowing characteristics:

Gravity, API 29.5 N, p.p.m. 67 S, p.p.m. 1700 Aromatics, vol. percent 32ASTM distillation, F.:

IBP% 416-508 20-40% 542-590 60-80% 630-668 90-EP (96%) 696-724 issubjected to a preliminary desulfurization by contact with a cobaltmolybdate on alumina desulfurization catalyst at a temperature of 650F., a pressure of 750 p.s.i.g., a hydrogen rate of 6000 s.c.f.b. and aspace velocity of 1.0. The hydrogen off-gas is scrubbed withdiethanolamine for removal of H S and combined with the desulfurizedhydrocarbon liquid with which it is charged to a hydrocracking zonecontaining a hydrocracking catalyst composed of 6% Ni and 19% W on asilica-alumina (87% silica, 13% alumina) base. The sulfur content of thehydrocarbon charge is 150 ppm. Hydrocracking conditions and yields aretabulated below.

Temperature, F. 640 Pressure, p.s.i.g 1500 Gas recycl rate, s.c.f.b 6300Space velocity (v./v./hr.) a- 1.0 Hydrogen consumption, s.c.f.b 2300115-200 F.:

Vol. percent 33.15

RON (+3 cc. TEL) 94.7 200-400 F.:

Vol. percent 63.70

RON (+3 cc. TEL) 82.4

The jet fuel product obtained from this operation is of low quality. The350-550 P. fraction has a smoke point of only 17 mm. and an undesirablyhigh aromatic content of 19 volume percent.

After the residual sulfur in the hydrocarbon charge has sulfided 85% ofthe metallic hydrogenation components of the catalyst, the yields andcharacteristics of the product are as follows:

Vol. percent 19.6 RON (+3 cc. TEL) 91.2 ZOO-400 F.:

Vol. percent 79.5 RON (+3 cc. TEL) 68.5 350550 F.:

Smoke point mm. 31 Aromatics, vol. percent 1 No real problem isencountered in determining the sulfur content of the catalyst. It iseasily calculated from the analysis of the sulfur present in the feedand the feed rate. The sulfur take-up by the metals of the hydrogenatingcomponent is practically quantitative. A substantial breakthrough ofsulfur indicates that sulfiding of the catalyst is essentially complete.In the sulfided form, as can be seen from the above example, thecatalyst produces a superior grade of jet fuel whereas, in the oxideform the catalyst produces a superior grade of gasoline.

Various modifications and variations of th invention as hereinbefore setforth may be made without departing from the spirit and scope thereofand therefore only such limitations should be imposed as are indicatedin the appended claims.

We claim:

1. A single-stage hydrocracking process for the conversion of ahydrocarbon liquid fraction into lighter hydrocarbons which comprisescontacting in a single hydrocracking stage a sulfur-containinghydrocarbon fraction having an initial boiling point not less than about400 F. in the presence of hydrogen under hydrocracking conditions with ahydrocracking catalyst comprising a hydrogenating component selectedfrom the group consisting of (1) nickel and tungsten (2) their oxidesand (3) mixtures thereof, recovering from the reaction product a motorfuel fraction having an end point of about 400 F., recycling to thehydrocracking zone a reaction product fraction boiling above the motorfuel range until at least of the hydrogenation components of thecatalysts are sulfided, recovering as product from the hydrocrackingreaction a motor fuel fraction and a jet fuel fraction, and recycling tothe hydrocracking zone that portion of the product boiling above the jetfuel range, the amount of sulfur introduced into the hydrocracking zonebeing maintained substantially constant throughout the process.

2. The process of claim 1 in which the hydrocarbon charge to thehydrocracking zone is subjected to a preliminary desulfurization.

3. The process of claim 1 in which at least of the metal of thehydrogenating component is sulfided.

References Cited UNITED STATES PATENTS 3,132,090 5/1964 Helfrey et a1.20889 3,213,012 10/1965 Kline et al. 208-111 DELBERT E. GANTZ, PrimaryExaminer.

A. RIMENS, Assistant Examiner.

1. A SINGLE-STAGE HYDROCRACKING PROCESS FOR THE CONVERSION OF AHYDROCARBON LIQUID FRACTION INTO LIGHTER HYDROCARBONS WHICH COMPRISESCONTACTING IN A SINGLE HYDROCRACKING STAGE A SULFUR-CONTAININGHYDROCARBON FRACTION HAVING AN INITIAL BOILING POINT NOT LESS THAN ABOUT400*F. IN THE PRESENCE OF HYDROGEN UNDER HYDROCRACKING CONDITIONS WITH AHYDROCRACKING CATALYST COMPRISING A HYDROGENATING COMPONENT SELECTEDFROM THE GROUP CONSISTING OF (1) NICKEL AND TUNGSTEN (2) THEIR OXIDESAND (3) MIXTURES THEREOF, RECOVERING FROM THE REACTION PRODUCT A MOTORFUEL FRACTION HAVING AN END POINT OF ABOUT 400*F., RECYCLING TO THEHYDROCRACKING ZONE A REACTION PRODUCT FRACTION BOILING ABOVE THE MOTORFUEL RANGE UNTIL AT LEAST 60% OF THE HYDROGENATION COMPONENTS OF THECATALYSTS ARE SULFIDED, RECOVERING AS PRODUCT FROM THE HYDROCRACKINGREACTION A MOTOR FUEL FRACTION AND A JET FUEL FRACTION, AND RECYCLING TOTHE HYDROCRACKING ZONE THAT PORTION OF THE PORDUCT BOILING ABOVE THE JETFUEL RANGE, THE AMOUNT OF SULFUR INTRODUCED INTO THE HYDROCRACKING ZONEBEING MAINTAINED SUBSTANTIALLY CONSTANT THROUGHOUT THE PROCESS.